Using column defaults

Column defaults automatically assign a specified value to a particular column whenever someone enters a new row into a database
table. The default value assigned requires no action on the part of the client application, however if the client application
does specify a value for the column, the new value overrides the column default value.

Column defaults can quickly and automatically fill columns with information, such as the date or time a row is inserted, or
the user ID of the person entering the information. Using column defaults encourages data integrity, but does not enforce
it. Client applications can always override defaults.

When default values are defined using variables that start with @, the value used for the default is value of the variable
at the moment the DML or load statement is executed.